The exposure of alkali metal silicate glass bodies to steam-containing environments at elevated temperatures to cause water to enter into the structure of the glass, thereby imparting thermoplastic behavior thereto, is known to the prior art in such literature as U.S. Pat. Nos. 3,498,802 and 3,912,481.
The former patent discloses the hydration of glass powders consisting essentially, in mole percent on the oxide basis, of 6-20% Na.sub.2 O and/or K.sub.2 O and 80-94% SiO.sub.2, the sum of those components totalling at least 90 mole percent of the compositions. The glass powders were subjected to gaseous environments containing at least 50% by weight steam at a pressure of at least one atmosphere and at a temperature commonly between about 100.degree.-200.degree. C. The hydrated powders could be formed into shapes of various geometries at temperatures of about 80.degree.-120.degree. C.
The latter patent describes a two-step method for hydrating glass bodies in steam-containing atmospheres to yield water-containing glass structures exhibiting thermoplastic characteristics. The process comprehends an initial hydration in a saturated or near saturated steam atmosphere at elevated temperatures, i.e., between about 100.degree. C. and the softening point of the glass, followed by a dehydration step at a lower relative humidity. The dehydration step can be so carefully conducted that the amount of water remaining in the glass structure can be rather rigorously controlled, thereby permitting close regulation of the degree of thermoplasticity imparted to the hydrated glass. Glass compositions operable in that invention consisted essentially, in mole percent on the oxide basis, of 3-25% Na.sub.2 O and/or K.sub.2 O and 50-95% SiO.sub.2, the sum of those components constituting at least 55 mole percent of the total composition.
The hydration of alkali metal silicate glass articles in aqueous solutions is disclosed in U.S. Pat. No. 3,948,629. That patent describes contacting fine-dimensioned glass bodies, customarily having thickness dimensions not exceeding about 5 mm., with an aqueous solution having a pH less than 6 and, preferably, less than 5 at a temperature in excess of 100.degree. C. and at a pressure of at least 20 psig. Since the solutions were acidic in nature, the patent noted an exchange taking place between H.sup.+ ions of the solution and Na.sup.+ and/or K.sup.+ ions in the glass. Also, where the aqueous solution contained K.sup.+ ions, the patent observed an exchange occurring between those K.sup.+ ions and Na.sup.+ ions where present in the glass. Glass compositions operable in that invention consisted essentially, in mole percent on the oxide basis, of 3-25% Na.sub.2 O and/or K.sub.2 O and 50-95% SiO.sub.2, the sum of those constituents constituting at least 55 mole percent of the total composition.